This invention relates to self-oscillating regulated converters and, more particularly, to a single-ended feedthrough type of converter. It is specifically concerned with frequency stabilization of the switching of such a converter.
Self-oscillating regulators or converters may be regulated by pulse width modulation of the switching device. In such arrangements a voltage regulation circuit monitors a voltage to regulated and modifies the duty cycle of the converter switching device to maintain the desired regulated output voltage. In a self-oscillating type converter the frequency tends to vary as the duty cycle is altered to maintain the regulated output voltage. In the past these frequency variations have either been tolerated or the frequency has been stabilized by means of an auxiliary outside frequency source to which the switching of the converter is synchronized. This synchronizing arrangement is undesirable because a separate source of oscillating frequency is needed, adding to the cost and complexity of the circuit.
Another frequency stabilization arrangement detects the ripple frequency of the output signal of the regulated converter and converts this to a frequency responsive control voltage. This frequency responsive control voltage is compared to a reference voltage and is used to modify the gain of the regulation feedback system to maintain the switching frequency at some desired value. This system, while advantageously eliminating the need for a separate frequency source, disadvantageously requires a separate frequency control feedback arrangement and sufficient ripple signal at the output of the regulated circuit to enable it to operate. Also the typical feedback arrangement to couple this ripple frequency to the frequency-to-voltage conversion circuit prevents the use of simple isolation techniques between the input and output of the converter circuit.
It is desirable to operate self-oscillating regulated converter circuits at a stabilized frequency. It is also desirable to achieve this frequency stabilization without the necessity of complicated feedback arrangements which eliminate isolation between the input and output of the circuit.